1. Field of Application
The present invention relates to a control system of a vehicle, which regulates engine speed and electric generator output voltage during engine idling. In particular the invention relates to such a system, incorporating a current detection apparatus which detects a level of current flow of a battery that is charged by output power from the electric generator of the vehicle.
2. Description of Related Art
A control system of a motor vehicle typically includes an engine control apparatus, i.e., engine ECU (electronic control function), one of whose functions is to regulates the engine speed to a specific value during engine idling. Such a system also includes an electric generator control apparatus which regulates the output voltage of the engine-drive electric generator (i.e., combination of an AC generator and rectifier, sometimes referred to as the alternator) that charges the vehicle battery and supplies various electrical loads. The output voltage is regulated by varying the level of field current (excitation current) of the electric generator, by varying the duty ratio of field current pulses, with that duty ratio being referred to in the following as the generation factor. At any specific rotation speed of the electric generator, the level of output power of the generator and the load torque applied to the engine by the generator are each determined by the generation factor. Hence, during engine idling, information expressing the generation factor is transmitted to the engine ECU, i.e., as load torque information.
If a sudden increase in the total electrical load occurs during engine idling, a high level of discharge current flows from the battery, causing a drop in the battery voltage. If the generator control apparatus immediately responds by increasing the generation factor, then the resultant increase in load torque may cause instability of the engine speed, and the engine may stall.
As described for example in Japanese Patent First Publication No. 5-272379 (pages 2-5, FIGS. 1-6), referred to in the following as reference document 1, a type of apparatus is known which detects the generation factor of the electric generator of a vehicle, and controls the rate of intake air flow to the engine during engine idling based on the detected value of generation factor, i.e., the working ratio of the electric generator.
Furthermore as described for example in Japanese Patent First Publication No. 2005-192308 (pages 6-9, FIGS. 1-7), referred to in the following as reference document 2, a type of apparatus is known whereby when an increase occurs in the level of load torque applied to the engine by the electric generator of a vehicle (due to an increase in electrical load), as the engine output power is being increased accordingly, the generation factor of the electric generator is controlled to prevent fluctuations in the battery voltage. After the required level of torque is reached, the engine speed is compared with a predetermined value, and if it is below that value, the generation factor of the electric generator is reduced and is thereafter gradually increased until the required engine speed is reached, thereby preventing excessive variations and overshoot of the engine speed.
Furthermore as described for example in Japanese Patent First Publication No. 9-107640 (pages 3-6, FIGS. 1-11), referred to in the following as reference document 3, a type of apparatus is known whereby when an increase occurs in the electrical load of a vehicle electric generator, the generation factor is controlled to increase in a specific manner, but whereby if the battery voltage should fall below a predetermined threshold value, the generation factor control is halted, i.e., the generation factor is set at 100% (maximum output power is produced by the electric generator).
However in the case of the apparatus of reference document 1, when generation factor control is being applied, it may be incorrectly judged that there is a sufficient level of electrical power being produced by the electric generator, and this may result in a delay in increasing the engine speed as required by an increase in the electrical load on the generator. Furthermore with such an apparatus, fluctuations in engine speed caused by increases in electrical load can be reduced, however no consideration is given to suppressing fluctuations in the battery voltage.
In the case of the apparatus of reference document 2, it is necessary to perform processing for continuously monitoring the engine condition, the battery condition, the electrical load condition, and the electric generator condition. Hence, the data processing load that is imposed on the engine control apparatus (engine ECU) become excessive. In addition, since it is necessary to connect a battery current sensor to the engine control apparatus via a long wiring harness that extends within the engine compartment, high levels of electrical noise may be induced in the wiring harness, resulting in errors in operation.
In the case of the apparatus of reference document 3, since the level of applied electrical load is detected based on the voltage of the battery, the control conditions will change over a long period of time due to change of the internal resistance of the battery. Hence it is difficult to ensure long-term stability of control.